As your link itself explains, the vast majority of those vacant properties are either a) holiday homes that are empty outside vacation season, or b) "areas with declining population where dwellings are simply abandoned by owners who can’t sell their property". Vacancy rates in major cities are remarkably low.
it may not be a big problem at present, as there is a huge real estate boom in Australia. But when there is an economic downturn these regulations are going to hit older areas extremely hard, just like they have in many other nations.
Property values in Australia declined by 4.5% last year. Forecasts are for around 5% growth this year in my city (Brisbane), but continued declining prices in Canberra, Melbourne, Hobart and Adelaide.
Huge real estate boom fizzled at the end of '09 / early 2010.
Those rates are voluntarily self-reported by rental property managers - there's a fairly clear conflict of interest.
According to the following Melbourne has a 5.9% vacancy rate. They use water usage data from the water companies for their analysis. (<50L/day = vacant property)
REIV vacancy rate is (unleased property on the books) / (property on the books).
It's always going to be an under-estimate of true vacancy due to properties that are empty full time and those that are privately managed and temporarily vacant.
Only one or two of the suburbs listed are actually considered inner city.
As someone who does live in the inner-city of Sydney and pay $3100USD/month for a shoebox. I would be incredulous if there were a large amount of vacancies beyond normal turnover.
There are usually bidding wars for property sales (most inner-city properties are sold by auction) and dozens of applications for rentals.
I've lived in the inner-west all my life & I know 5 or so squatters. Yep. There are vacant buildings everywhere you probably just don't know it. There's a whole world outside the market & we need to encourage this sort of thing, or else a city becomes locked into mortgages with little job flexibility. The ability to live cheaply in a city is very important. High costs to maintain a basic lifestyle mean less risk taken, less businesses started, less innovation, less arts. In total contrast to Sydney is Berlin: high unemployment, very low cost of living, tons of start-ups, tons of arts.
I'm also from Perth, but I don't see urban decay "all over the city". The worst (and only) place I probably had the feeling of some urban decay was Ellenbrook.